More robust findScalaHome in bash scripts. See SI-5792

Allows multiple absolute or relative symlinks by jumping through
the directories while following the links.
all treemakers need positions for unreachable error
construct typed trees in TypeTestTM
patmatdebug
support for repeated approximation of treemakers
Unreachability analysis for pattern matches

Analyze matches for unreachable cases.

A case is unreachable if it implies its preceding cases.
Call `C` the formula that is satisfiable if the considered case matches.
Call `P` the formula that is satisfiable if the cases preceding it match.
The case is reachable if there is a model for `-P /\ C`.
Thus, the case is unreachable if there is no model for `-(-P /\ C)`,
or, equivalently, `P \/ -C`, or `C => P`.

Unreachability needs a more precise model for type and value tests than exhaustivity.
Before, `{case _: Int => case 1 =>}` would be modeled as `X = Int \/ X = 1.type`,
and thus, the second case would be reachable if we can satisfy `X != Int /\ X = 1.type`.
Of course, the case isn't reachable, yet the formula is satisfiable, so we must augment
our model to take into account that `X = 1.type => X = Int`.

This is done by `removeVarEq`, which models the following axioms about equality.
It does so to retain the meaning of equality after replacing `V = C` (variable = constant)
by a literal (fresh symbol). For each variable:
 1. a sealed type test must result in exactly one of its partitions being chosen
    (the core of exhaustivity)
 2. when a type test is true, tests of super types must also be true,
    and unrelated type tests must be false

For example, `V : X ::= A | B | C`, and `A => B` (since `A extends B`).
Coverage (1) is formulated as: `A \/ B \/ C`, and the implications of (2) are simply
`V=A => V=B /\ V=X`, `V=B => V=X`, `V=C => V=X`.

Exclusion for unrelated types typically results from matches such as `{case SomeConst =>
case OtherConst => }`. Here, `V=SomeConst.type => !V=OtherConst.type`. This is a
conservative approximation. If these constants happen to be the same value dynamically
(but the types don't tell us this), the last case is actually unreachable. Of course we
must err on the safe side.

We simplify the equality axioms as follows (in principle this could be done by the
solver, but it's easy to do before solving). If we've already excluded a pair of
assignments of constants to a certain variable at some point, say `(-A \/ -B)`, then
don't exclude the symmetric one `(-B \/ -A)`. (Nor the positive implications `-B \/ A`,
or `-A \/ B`, which would entail the equality axioms falsifying the whole formula.)

TODO: We should also model dependencies between variables: if `V1` corresponds to
`x: List[_]` and `V2` is `x.hd`, `V2` cannot be assigned at all when `V1 = null` or
`V1 = Nil`. Right now this is implemented hackily by pruning counter-examples in exhaustivity.
Unreachability would also benefit from a more faithful representation.

I had to refactor some of the framework, but most of it is shared with exhaustivity. We
must allow approximating tree makers twice, sharing variables, but using different
approximations for values not statically known. When considering reachability of a case,
we must assume, for example, that its unknown guard succeeds (otherwise it would wrongly
be considered unreachable), whereas unknown guards in the preceding cases must be
considered to fail (otherwise we could never get to those case, and again, it would
falsely be considered unreachable).

Since this analysis is relatively expensive, you may opt-out using `-Xno-patmat-analysis`
(or annotating the selector with @unchecked). We hope to improve the performance in the
near future. -Ystatistics has also been extended to provide some numbers on time spent in
the equality-rewrite, solving and analyzing.
fixing bug found by unreachability
allow disabling patmat analyses: -Xno-patmat-analysis
Add Hashing and Equality typeclasses.

Modify TrieMap to use hashing and equality.

Modify serialization in TrieMap appropriately.
Remove Equality in favour of Equiv.

Make Equiv serializable.
Fix `Hashing`.

Move `Hashing` to `scala.util.hashing`.
Adde `Hashing.Default` to `Hashing` companion object.
Change `TrieMap` to autoswitch from `Hashing.Default` to `TrieMap.MangledHashing`.
Made parser less hostile to inspection.

By annotating all the boolean method arguments.
Closes t5399. Review by adriaanm
Merge pull request #658 from odersky/ticket/5399

Fix for SI-5399.
Merge pull request #657 from paulp/parser-booleans

Made parser less hostile to inspection.
Merge pull request #648 from pvlugter/issue/5792

More robust findScalaHome in bash scripts
incorporate @retronym's review comments
SI-5683 Fail gracefully when transposing a ragged type arg matrix.

The code used to do this, until `transpose` starting throwing IAE
rather than AIOOBE.

Symptomatic treatment only: The reported crasher now infers ill-kinded
type args and reports an error.
Don't compute least upper bounds for expressions in statement positions inside blocks.

This may save huge amount of time (Fixes SI-5862) for complicated lubs. I had to remove the a check in adapt for
the part that transforms <expr> into { <expr>; () } when the expected type is Unit. The reason is in the
code.

As a side effect, we get more warnings for pure expressions in statement positions (see the change in the test file).
Merge pull request #650 from adriaanm/topic-virtpatmat

Unreachability analysis for pattern matches

Thanks for reviewing, @retronym!